1. Field of the Invention
The present invention relates to a reader, that is, apparatus which converts information of an original surface or a surface to be examined into electrical signals and reads out the same. The apparatus to which the present invention pertains is usable together with image information processing apparatus such as facsimile, laser beam printer, ink jet printer or the like and also may be utilized together with such apparatus used for inspecting a flaw or flaws on the surface of an object.
For the purpose of this specification, the term "original surface" should be understood to include also such surface which is to be examined or whose flaw is to be inspected.
2. Description of the Prior Art
There are various types of apparatus which optically read information of an original surface and in which a photoelectric sensor is used as light detector. However, in the past, it was very difficult to obtain photoelectric sensor of high resolving power satisfactorily useful in the information reading apparatus. There was available only such solid photographing element of several centimeters in length an example of which is that called Charge Coupled Device (CCD). For that reason, in order to read information on an original surface it was required to use a reducing optical system with an optical axis in the apparatus and carry out reading of the information by forming a reduced image of the original surface on such solid photographing element.
However, such known apparatus in which a reduced image of an original surface is formed on a solid photographing element of high resolving power by the use of a reducing optical system with an optical axis had various disadvantages. One of the disadvantages was a long conjugate distance required for reducing image formation between the original surface and the solid photographing element. Because of the long conjugate distance, the apparatus had to have a larger size as a whole. Secondly, the finite opening of the reducing optical system has resulted in a decreased quantity of the image plane light on the solid photographing element surface, which has, in turn, led to a reduced sensitivity. In addition, since the quantity of image plane light decreased gradually as it departed from the optical axis, it was impossible to maintain the sensitivity at a constant level.
With the recent advancement of the technique in the art there have been developed those photoelectric sensors of high resolving power which allow a very long structure while each sensor element constituting the minimum unit capable of separating and reading information light in the structure are very small. As an example, mention may be made of a thin film photo diode array formed by Se-As-Te noncrystalline semiconductors. Thus, it has become possible to realize a novel form of apparatus which uses these photoelectric sensors instead of the reducing optical system to read information on an original surface. This novel type of information reading apparatus can be designed very compactly as disclosed, for example, in Japanese Laid Open Patent Application No. 104808/1977.